1. Technical Field
The present invention relates to an image processing apparatus, a copier, and image processing method and program.
2. Related Art
In the past, a serial printer such as an ink jet printer, a dot impact printer, and a thermal printer was known. Such a type of serial printer performs a printing operation on a paper sheet by a series of operations in which ink is ejected on the paper sheet while a printing head is moved in a main scanning direction (for example, right and left directions), and then the paper sheet is transported in a sub-scanning direction (for example, front and rear directions) by a transport roller. Moreover, as a method of moving the printing head, such a type of serial printer uses a method called a logical seek. The logical seek refers to a method of minimizing movement of the printing head before the next time movement of the printing head. For example, when first to third character string existence areas A1 to A3 extended in right and left directions of a paper sheet P are arranged sequentially from the front of the paper sheet P, as shown in FIG. 11, the logical seek will be described. In FIG. 11, white arrows represent a movement direction of a printing head PH and black arrows represent a relative movement direction of the printing head PH for the paper sheet P (practically, the printing head PH is not moved in the front and rear directions, but the paper sheet P is transported in the front and rear directions). First, the printing head PH ejects ink on the first character string existence area A1 while moving in the left direction from the right end which is a home position, and then moves to the left end of the second character string existence area A2 without ejecting ink. Afterward, the paper sheet P is transported in the front direction. Subsequently, the printing head PH ejects ink on the second character string existence area A2 while moving the right direction from that position, and then moves to the right end of the third character string existence area A3. Afterward, the paper sheet P is transported in the front direction. Subsequently, the printing head PH ejects ink on the third character string existence area A3 while moving the left direction from that position. By using such a logical seek, it is possible to shorten movement period of time of the printing head, and furthermore shorten printing period of time. This type of logical seek is disclosed in JP-A-9-252386.
However, the printing period of time may not be shortened in a case where image data obtained by scanning an image by a scanner is printed by the serial printer using this logical seek. That is, in a case where the obtained image data have isolated points caused by dust and the like in areas other than the first to third character string existence areas A1 to A3 which are originally printed areas, an advantage of the logical seek may not be obtained. That is because the movement period of time of the printing head PH becomes longer, as shown in FIG. 12. In order to solve this problem, removing the isolated points can be taken into consideration. However, for example, as shown in FIG. 13, the upper portion (within a circle in FIG. 13) of a character b in a character string “abcxyz” protrudes more upward than the upper portions of the other characters, and the lower portion (within a circle in FIG. 13) of a character y thereof protrudes more downward than the lower portions of the other characters. Consequently, when the isolated points are removed in every band (each of which are constituted by several lines), the upper portion of the character b or the lower portion of the character y is determined as the isolated point. Therefore, a problem arises in that the upper portion or the lower portion thereof may not be printed.